"Hauling" is a G-Rated way of saying "Hauling @SS" It is an idiom meaning "to move quickly or to hurry," So when you hear someone say "that coaster was hauling!" They are meaning its running fast or faste rthan normal.
If you want to see a good example of what Kw6s is referring to, watch the Storm Chaser video from opening day vs now. Notice the difference in speed on the turn into the brake run.
3 years ago:
this year: